The present invention relates to an adjustable stand, particularly for photographic and cinematographic use but also suitable for use in the musical field and in furniture of the type comprising a telescopic stem with first and second stem elements which are slidable relative to one another, and with a locking device for firmly fixing the stem elements to one another, the locking device including a collar which is connected to the first element of the stem and surrounds the second element at least partially, as well as clamping means for the collar for tightening it from a inoperative position in which the second stem element is slidable relative to the first to an operative position in which the second stem element is fixed firmly to the first element by means of the collar.
Stands of the aforementioned type are widely known on the market; for example, tripods with collars which are clamped adjustably by screw clamping means like a conventional clamp are typical.
A main disadvantage of these stands lies in the need to operate the clamping means of the collar manually each time the sliding of the stem elements is to be locked or, conversely, unlocked in order to adjust the height of the stand.
Another example of solutions offered by the prior art is constituted by stands for photographic or cinematographic use which are marketed by the U.S. company Teledyne Industries, Inc.
The stands of this second example have devices for locking the sliding of the stem elements, based on the friction produced between the second stem element and a rubber-coated metal ring. A screw system enables the angle of intersection of the axes of the ring and of the stem elements to be adjusted so as to vary the friction between the second stem element and the ring. The optimal adjustment is achieved when the overall lead bearing on the second stem element is balanced by the aforesaid friction. Although the system is efficient, it is, however, quite dangerous in operation. In fact, it is subject to possible accidental loosening of the device for locking the stem. Anyone may thus, even inadvertently, loosen with a single hand the screw system which governs the positioning of the ring and consequently cause the second stem element to drop suddenly.